Transcription factors are well known proteins involved in the initiation of transcription. They have been studied intensively in many different organisms and have also been described in fungi. Dhawale and Lane (NAR (1993) 21 5537-5546) have recently compiled the transcription factors from fungi, including the filamentous fungi.
Many of the transcription factors are regulatory proteins; they bind to the promoter DNA and either activate or repress transcription as a response to stimuli to the cell.
The expression of the .alpha.-amylase gene in A. oryzae is regulated in response to the available carbon source. The gene is expressed at its maximum when the organism is grown on starch or maltose (Lachmund et al. (1993) Current Microbiology 26 47-51; Tada et al. (1991) Mol. Gen. Genet. 229 301-306). The expression of .alpha.-amylase is regulated at the transcriptional level as shown by Lachmund et al. (supra), which strongly suggests that transcription factors are involved in the regulation, but so far no gene for such a factor has been identified.
The promoter of the .alpha.-amylase gene has been studied by deletion analysis (Tada et al. (1991) Agric. Biol. Chem. 55 1939-1941; Tsuchiya et al. (1992) Biosci. Biotech. Biochem. 56 1849-1853; Nagata et al. (1993) Mol. Gen. Genet. 237 251-260). The authors of these papers propose that a specific sequence of the promoter is responsible for the maltose induction. Nagata et al. (supra) is used this sequence as a probe in a gel shift experiment to see whether any proteins from A. nidulans nuclear extracts were able to bind to the promoter sequence. Three such proteins were found, but no involvement of these proteins in expression was shown. None of the proteins have been purified or identified by other means. Their genes likewise remain unknown.